Gun Tap VS Spiral Tap

Yep. The standard straight plug tap needs to be reversed every turn or so, to break the chips, and backed out to clear the chips. Gun taps are far better.

Yes.

When hand tapping, I often use a gun tap in a short blind hole, but with care. I manually remove the ball of stringy chips, then finish the job with a bottoming tap.

If the blind hole is deep enough, one can skip the followup with the bottoming tap, but one should always remove the ball of chips, lest it get into the threads and jam the screw.

Joe Gwinn

You need to look into Form Taps. They don't have any chips. The drilled hole is larger, and the tap FORMS the threads by squeezing the metal into the thread form.

The threads can be much stronger, and the taps themselves are much stronger!

Not much more force to tap, but the taps last and last... You may never want to go back to cutting taps.

I do too. I found that a little right angle bent on the end of a piece of mig wire makes a great thing to pull that "ball of chips" out on any thing bigger that a #8. I bend a loop about 1/2" on the other end to hold and twist CCW with.

Oh I prefer to call them "spiral point" and "spiral flute" ...lew...

GREAT for aluminum but with the tight and odd size requirement for the tap drill, I don't use them on steel. For aluminum the tolerance can be let a little looser. :-) ...lew...

The next thing to consider is "stir-welding". That form drill is pretty slick but I wonder if its practical for manual operation. Oh! and how high a speed is required for a #4 screw? ...Lew...

Not unless you are looking for lots of practice at removing broken taps. :-)

Standard taps require frequent reversal of the tap to break off chips before they get too long and clog the hole. Tapping heads don't do that reversal normally. If you back out frequently enough with a slow enough RPM, I guess you might get away with it, but I wouldn't bother.

Correct.

Correct.

Correct.

You can use the gun taps with blind holes -- *if* there is enough extra depth to accept the chips beyond the maximum required thread penetration. I've done this with threading through holes (well, holes intended to be through when things are parted off) for multiple identical parts on a lathe with a bed turret. Drill deep, tap deep enough, and part off. Every so often, I had to do another parting about

3/4" past the first when the hole started to walk too far off center, as each hole was a continuation of the previous, while the second part off allowed me to make a fresh start. Next time I set up for these, I intend to try the thread forming taps, which should save me a few inches over the length of a 6' bar. :-)

I've not used the spiral flute taps, so I don't know for sure, but my feeling is that with tougher materials, the spiral will tend to unwind a little changing the effective thread pitch, and perhaps causing it to bind when backing it out.

Of course, for *through* holes, another option which is nice if the holes are not too deep are the combination drill and tap (where the tap has to be spiral to match the spiral of the drill part).

So -- you have my opinion. It will be interesting to compare that to those of others.

Enjoy, DoN.

Spiral FLUTE taps are what you are talking about. They look like twist drills with threads in them, and bring the chips up the same way a drill bit does. There are different from spiral POINT taps.

My experience with spiral flute taps is they are great for shallow blind holes or through holes in thin material. They don't work well on DEEP blind holes, like deeper than 5X diameter or so. The chips eventually bind the tap. Much better to drill deeper and use a gun tap for the deep holes. A spiral point tap also pushes the chips ahead.

Jon

--Yah that might be an issue. I run #10s at about 2800rpm; 1/4" is something like 2200 IIRC. And forget about doing it with a hand drill: you definitely need the force multiplier of a feed handle; I do my stuff on a Bridgeport. Still and all it's an awesome process.